External mounted amplifiers (EMAs), such as tower mounted amplifiers (TMAs) and ground mounted amplifiers (GMAs) are a special class of low-noise amplifier that are mounted external to base station receivers and as close as possible to radiating antennas. EMAs, including TMAs and GMAs, are typically positioned outside of a base station receiver and are not tied electrically to the receiver for gain control. TMAs and GMAs are essentially the same, except for the mounting location of each type of EMA external to the radiating antennas. TMAs are mounted on towers and GMAs are mounted on the ground. GMAs are used to condition radio frequency (RF) signals received at the radiating antennas before the signals are sent to the receiver in the base station.
Some TMAs and GMAs include filters to limit the bandwidth that is amplified and to keep the corresponding transmitter signal from overloading the respective TMA or GMA. Filters are sometimes used to improve the signal to noise ratio (SNR) of signals received at radiating antennas by filtering noise and interference received with the signal at TMAs and GMAs. Improved SNRs enable the receiver to better demodulate the desired signals. TMAs and GMAs employ both low noise amplifiers and filters to improve the signal quality before presenting the desired signals to the receivers. Filters only remove the RF signals outside of the filters' pass-band. Thus, interferers within the filters' pass-band pass through unaffected.